Polymer foams containing filler materials, such as particulate filler materials, are widely known and used. Closed cell rigid polymer foams, especially polyurethane and polyisocyanurate foams containing particulate filler, such as carbon black or other particulate filler, are widely used for thermal insulation purposes. Foams of this type and their use for thermal insulation purposes are disclosed, for example, in U.S. Pat. No. 5,604,265 to DeVos et al. Also, in U.S. Pat. No. 5,373,026 to Bartz et al, polymer foam structures incorporating carbon black filler are taught for thermal insulation purposes.
In polymer foams such as, for example, polyurethane and polyisocyanurate foams, cost reduction and/or thermal insulation improvement can be achieved by improving dispersion of filler material in the foam, by controlling foam cell size, and/or by increasing infrared absorption. The windows of the cell structure are believed to be significantly transparent to infrared radiation. The thermal conductivity of these foams should be improved by increasing the infrared absorption of the cell windows. One way to do this is to add infrared absorbing materials, such as carbon black, to the foam. However, the distribution of carbon black in these foams typically is poor, such that the majority of carbon black resides in the struts of the foam. The windows of the foam may contain little or no carbon black. In fact, it is doubtful that prior work has achieved carbon black concentrations in the windows equivalent to the carbon black concentration found in the struts.
There is a recognized need in the polymer foam industry for foams having improved performance characteristics and/or reduction in the cost and complexity of manufacturing such foams. In certain applications, such as foam insulation and in refrigeration units or other appliances or for architectural insulation, this need has been increased due to the loss of insulation performance caused by the reduction or elimination of halogenated blowing agents. Some substitute blowing agents are found to produce foams having higher thermal conductivity. Hence, there is an increased need for lowering the thermal conductivity of polymer foams suitable for use in various insulation applications, particularly appliance and architectural thermal insulation uses.
It is an object of the present invention to provide improved polymer foams. It is a particular object of the invention to provide polymer foams having lower thermal conductivity, or, the alternative, lower thermal conductivity per unit cost of the foam. In accordance with certain preferred embodiments of the invention, it is an object to provide rigid, closed cell polymer foams incorporating chemically modified carbonaceous filler materials not previously used for such applications, and being suitable for various insulation purposes. These and additional objects and advantages of the present invention will be apparent to those skilled in the art from the following disclosure of the invention and detailed description of certain embodiments.